AFGL 618 is a carbon-rich post AGB star/protoplanetary
nebula (PPN), and is surrounded by extremely large
circumstellar dust shells, containing the fossil record of
its AGB mass loss. This dust shell ahs been observed at
120\mum and 180\mum by ISOPHT. We present results of
radiative-transfer (RT) modeling of these dust shells, using
the 1-d RT code DUSTY. While AFGL 618 is clearly
axisymmetric close to the central star, this axisymmetry is
contained well within the PSF of the ISO FIR observation.
Our models are intended to determine several parameters AFGL
618 which are not currently wll constrained; among tehse
being distance, gross dust distribution, stellar
temperature, inner dust shell radius, dust grain size
distribution, and dust grain composition. While there is
some degeneracy within the models providing good fits to the
data, some general results have emerged. We found that the
optical depth of the dust shell in the mid-IR
(\tau9.7\mum) is between 3 and 7. Furthermore, we
have found that in order for the modeled brightnesses to
match the observational data at both wavelengths (for the
central region), it is necessary to include a considerable
amount of crystalline dust (graphite and SiC) into the
circumstellar shell in addition to amorphous carbon. Finally
we show that the radial density distributions needed to
match the observations are indicative of either constant
mass-loss rate throughout the histor of the shell, or
increasing mass-loss rates for the last few hundred years of
the AGB. This increasing mass loss is interpreted as the
superwind phase.